The invention concerns a method and a connecting system for the joining of moulded parts.
A method of known art for the joining of moulded parts is so-called punch riveting with a solid rivet. Punch riveting often finds application in automotive construction and more generally in the sheet metal processing industry on thin sheets of a very wide variety of metallic materials. Suitable materials are, for example, light metals such as aluminium and magnesium, or ferrous metals such as steel. However, punch riveting also allows the joining of a metallic moulded part to a plastic-based moulded part and thus the manufacture of hybrid joints. By virtue of the relatively low strength of the joint under tensile head loading in comparison to the shear strength, a punch rivet joint is often used only at locations that are subjected to shear loading.
Punch riveting with a solid rivet is based on a combined perforation and pressure forming of the moulded parts, in which a rigid solid rivet generates a force and a form fit point joint. For purposes of manufacturing the joint the moulded parts are fixed on a die by means of a hold-down device. The punch rivet is then driven by means of a riveting header through the moulded parts and in this manner the latter are perforated. As a result of the contour of the die and the pressure force applied via the riveting header and the hold-down device the material of the moulded part on the die flows into a peripheral groove on the shank of the punch rivet. The flow of material is thereby opposed to, or transverse to, the punching direction. At the same time the head of the punch rivet is pressed against the riveting header-side moulded part, or if it is a countersunk head, it is impressed into the riveting header-side moulded part. The main component of the strength of the joint under tensile head loading is found in the form fit, which is generated from the undercut on the head of the punch rivet and the filling of the groove on the shank of the punch rivet. In order to increase the form fit component for higher load-bearing capacities, so-called multi-region rivets can be deployed. The multi-region rivets have a plurality of parallel shank grooves, which increase the form fit when the rivet is in the set state. Examples of multi-region rivets are described in the U.S. Pat. Nos. 6,527,490 B1 and 4,978,270. However, in general it has been shown that the filling of the shank grooves is strongly dependent on the respective material of the moulded parts. In DE 10 2010 000 500 A1 it is therefore proposed that for purposes of applying punch rivets to all punchable materials, the punch rivet should be locked outside the moulded parts. For this purpose a locking collar is set in place on a shank section led out through the punched hole, and is pressed together with a shank groove by means of an axial upsetting force.
An alternative joining method for purposes of connecting sheet metal-type moulded parts is joining by means of a locking collar pin. In this method a hole is introduced into the moulded parts before the actual riveting operation, through which hole the locking collar pin is then led out and subsequently locked with a locking collar squeezed onto the locking collar pin. The result is a joint with a high load-bearing capacity, which by virtue of parallel locking grooves has a high tensile head strength and also has high reliability in the locked state. However, by virtue of the separate perforation operation before the riveting process, this method is more labour-intensive than the punch rivet method.